The present invention relates to an optical fiber ribbon having an intermittent fixing structure in which adjacent optical fibers are intermittently connected together via connecting portions, and relates to an optical fiber cable housing the optical fiber ribbon.
There has been an increased demand for higher density and reduction in diameter in the technical field of optical fiber cables. As an example of a method for achieving higher density and reduction in diameter, there is proposed a method for reducing the outer diameter of optical fibers from 250 μm, which is a presently-used size, to 200 μm or smaller (for example, described in Japanese Patent No. 3058203 (Patent Literature 1). An optical fiber ribbon using this method has a structure in which a plurality of optical fibers each having the outer diameter of 200 μm or smaller are arranged in parallel, and the entire circumference of the optical fibers is covered with ultraviolet curable resin.
With the optical fiber ribbon described in Patent Literature 1, however, an intermediate branching operation is difficult when laying optical fibers into residences of subscribers. In order to lay the optical fibers into the residences of subscribers, a cover layer entirely covered with the ultraviolet curable resin is required to be removed in the middle of the cable so that particular optical fibers are only extracted from the plurality of optical fibers. Since the entire circumference of the plural optical fibers is covered with the ultraviolet curable resin, the removal of the ultraviolet curable resin is difficult and the particular optical fibers are not easily removed from the other optical fibers. Further, in the optical fiber ribbon described in Patent Literature 1, the entirely-covered cover layer increases the thickness of the optical fiber ribbon by the thickness of the cover layer, which decreases the packaging density thereof.
Japanese Patent No. 4143651 (Patent Literature 2) teaches an optical fiber ribbon capable of solving these problems. This optical fiber ribbon does not have a structure in which optical fibers are entirely covered with resin, but has an intermittent fixing structure in which adjacent two optical fibers of three or more of optical fibers arranged in parallel are connected together with resin. The intermittent fixing structure of the optical fiber ribbon described in Patent Literature 2 contributes to easy intermediate branching operation and has the advantage of higher density since the number of connecting portions is smaller than that in the structure of Patent Literature 1.